Semiconductor devices have source/drain regions and gate electrodes connected to metal wirings by contact structures. A typical contact structure may be fabricated by forming an interlayer insulating film composed for example, of SiO2, over the semiconductor device and selectively removing a portion of the insulating film to form a contact hole. A metal composite film composed, for example, of titanium (Ti), titanium nitride (TiN) and aluminum (Al) are successively deposited on the surface of the contact hole. After that, the contact hole is filled with a metal, such as tungsten to complete the contact.
During contact fabrication, the Ti film reacts with silicon atoms of the source/drain region or gate electrode during a heating process after deposition to form a silicide which serves to decrease the contact resistance between the source/drain region or gate electrode. The TiN film serves as an anti-diffusion film to prevent mutual movement of silicon atoms and aluminum atoms. The Al film constitutes a main body of the metal wiring and serves to conduct an electric current at a low resistance.
Sometimes, during the contact fabrication process, defective contacts are produced. The defective contacts are often characterized by larger leak currents. The larger leak currents may also be due to defects in the structures of the semiconductor device, such as the gate oxide. Hence, defective contacts and/or device structures may be distinguished from normal contacts and device structures by measuring contact current leakage.
Unfortunately, conventional defect detecting techniques, such as voltage contrast (VC) on a scanning electron microscope (SEM), can not distinguish between the micro-current leakage of normal and defective contacts and/or device structures. Moreover, the submicron size of the contact structures makes it impossible to use traditional probing techniques to measure the contact leak current.
Accordingly, a method is needed for measuring contact leak current of semiconductor device contacts to distinguish between the micro-current leakage of normal and defective contacts and/or device structures.